Seroincidence of HIV infections continue to occur among men who have sex with men (MSM) at an alarming rate. Recent reports have found that many new infections occur within primary partner relationships. Although a great deal of prevention research has focused on MSM, there is little known about relationship factors that contribute to sexual risk among male couples. Even less is known about agreements couples make about sex outside the relationship. The proposed three-phase study combines qualitative and quantitative methods. Phase I is a qualitative study (n = 45) that will confirm and elicit relationship variables associated with agreements couples make about sex outside the relationship. Phase II (n = 200) will develop and pilot test measures addressing agreements couples make about sex outside the relationship. Phase III (n = 450) is a cross-sectional study that will design and test a MSM "couples" model of sexual risk-taking behavior. Serodiscordant (where one partner is HIV seropositive and one partner is HIV seronegative) and seroconcordant (where both partners are seronegative or both are seropositive) couples will be included in the study. The specific aims of the proposed study are to: (1) Explore factors associated with agreements MSM couples make about sex within and outside their relationships (Phase I). (2) Explore the role serostatus concordance versus discordance has on agreements couples make about sex within and outside their relationships (Phase I). (3) Develop and pilot test a new "agreements about sex" scale (Phase II). (4) Examine the role of within and between couple differences in intimacy, communication, agreements about sex, perception of risk, personal dispositions, relationship motives and social norms, in predicting sexual risk-taking among couples (Phase III). (5) Examine the influence each partner has on his own and his partner's association between intimacy, communication, agreements about sex, perception of risk, personal dispositions, relationship motives, social norms and sexual risk-taking behavior (Phase III). This study will add to existing theories of behavior change by focusing on the couple rather than individuals and by identifying key variables contributing to risk among couples. Data from this study will be instrumental in developing tailored interventions for gay male couples at risk for HIV and related infections.